As is well-known, circuit breakers provide automatic power interruption to a monitored load when undesired fault conditions, such as an overload of current or a short circuit, occur. A circuit breaker is typically wired between a load and a power source on a line conductor. The load receives power from the line conductor from the circuit breaker and is directly connected to a ground conductor. A neutral rail or conductor is also connected to the power source through the circuit breaker to provide a return for the current back to the power source. A circuit breaker is an automatically operated electro-mechanical device designed to protect the load from damage when a fault occurs by breaking the connection on the line conductor to the load. A typical circuit breaker has a load connector and a line connector with a break mechanism interposed between the load connector (connected to the power input of a load device) and the line connector (connected to the power lead of a power source such as a panel board). Various fault conditions trip the circuit breaker thereby interrupting power flow between the load and the power source. A circuit breaker can be reset (either manually or automatically) to resume current flow to the load.
Circuit breakers have mechanical mechanisms that are tripped by overcurrents to interrupt power to a load. An overcurrent may be detected when the fault current generates sufficient heat in a bimetal strip causing the strip to bend. The mechanical deflection triggers a trip mechanism that includes a spring-biased trip lever to force a moveable contact attached to a moveable conductive blade away from a stationary contact, thereby breaking the circuit.
Other fault conditions may also include, for example, arc faults and ground faults which also require the interruption of the connection between the load and the power source. Such conditions require sensing electrical signals on the connection rather than a mechanical trigger. In order to provide protection against such faults, a circuit breaker may therefore also include electronic components that detect such fault conditions and cause the circuit breaker to electronically trip. The electronic components may be provided in addition to the thermal-magnetic tripping components. The electronic components process a signal output of a sensor that monitors current flowing in the circuit breaker to determine whether one of the fault conditions is present and to generate a fault signal and/or a trip signal. In response to the generation of a fault signal, a plunger is electrically activated trigger the trip mechanism and thereby interrupt power to the load.
The above mechanisms provide protection against fault conditions which occur from the line and neutral conductors that carry the power to the load. However, the neutral conductor also requires protection against accidental disconnection (open-neutral conditions) that will create a dangerous ungrounded open circuit for the load. For example, a potentially dangerous situation results from an open-neutral condition due to the panel board neutral connection of an electronic circuit breaker becoming unplugged while the line side connection between the circuit breaker and load remain connected. The situation is dangerous because in electronic circuit breakers, the electronics of the circuit breaker are sometimes powered between the line and neutral conductors (line-to-neutral powered) and will not function if the neutral connection between the circuit breaker and the panel in which the breaker is installed is lost. If the electronics of the circuit breaker are not powered, the circuit breaker will lose its advanced protection functions such as detection of ground faults or arc faults. Also, voltage may be supplied to loads which appear to be off and do not run because no current can flow, and because the neutral side of the circuit, which is normally near ground potential, is now near the potential level of the line power supply. In certain situations, there may be increased risk of losing this connection with a plug-on panel neutral connection which could be inadvertently disconnected if the circuit breaker is inadvertently bumped during service of an adjacent circuit breaker causing the panel board neutral connection to become unplugged.
Therefore there is a need for a circuit breaker that will be tripped when the neutral connection becomes unplugged. There is also a need for a mechanism that prevents the breaker from being switched to an on position if the neutral connection is not made to insure that the advanced electronics protection features are active.